During a nitration process to produce a desired chemical product, such as nitrotoluene or nitrobenzene, nitrophenolic by-products are produced. These nitrophenolic by-products are usually present in the form of a mixture of di- and tri-nitrophenols and/or di- and tri-nitrocresols. The by-products are separated from the desired nitrated product by washing. The by-products are then present in the wash water or waste water stream which must be disposed of in some environmentally safe manner.
Various processes are known in the art for disposing of waste water containing nitrophenolic materials. One process which has been used for disposing of nitration waste water is to collect the waste water from the nitration washers in a lagoon and adjust the pH of the waste water to approximately 1.5 to cause substantially all of the phenolic compounds present in the waste water to indiscriminately precipitate. The precipitate is not recovered for reuse. Due to environmental concerns and the increasing number of chemical by-products, however, lagooning is no longer considered a viable environmentally safe method of disposal.
Currently contemplated methods of waste water disposal require removal of the nitrophenolic by-products before the waste water can be disposed of to avoid damage or potential damage to the environment. However, the by-products are not recovered in a substantially pure form suitable for commercial sale, but simply separated from the waste water indiscriminately to put the waste water in a suitable form for disposal. The recovered by-products are disposed of separately from the water, such as by incineration. For example, U.S. Pat. No. 4,597,875 discloses the production of dinitrotoluene with the concurrent production of nitrophenolic by-products, i.e. nitrocresols and picric acid. Prior to disposal of the waste water, the by-products are removed from the waste water. The waste water is first contacted with an alkaline material to convert the by-products to water soluble salts. An organic and aqueous phase are generated. The aqueous phase, which contains nitrophenolic materials, is separated out and treated with an acid to convert the salts to a water insoluble material. The water insoluble materials separate into an organic phase containing the converted nitrophenolic materials and an aqueous phase containing water soluble salts. The organic phase, due to its lower water content, can then be incinerated to dispose of the contaminants.
U.S. Pat. No. 655,117 discloses a process for separating an isomeric mixture of meta- and para-cresols. The process of separation is based on the ready solubility of m-cresol-sulphonic acid in sulfuric acid and the substantial insolubility of para-cresol-sulphonic acid in sulfuric acid. The cresol mixture is heated with concentrated sulfuric acid to convert the cresols to their respective sulphonic acid forms. The resulting products are allowed to stand in order to allow the para-cresol-sulphonic acid to crystalize out of the mixture. The crystalized cresol is then removed from the mother liquor by filtration. Thereafter, the sulfuric acid is split off from the cresol by superheated steam in order to obtain the pure para-cresol. The m-cresol remains in the mother liquor.
U.S. Pat. No. 1,025,615 discloses the separation of meta- and para-cresols using sulfuric acid by converting the cresols to sulphonic acids. The '615 patent is similar to the '117 patent noted above, except that the meta-cresol-sulphonic acid is crystalized and recovered in the process disclosed rather than the para-cresol-sulphonic acid which is recovered in the process of the '117 patent.
U.S. Pat. No. 1,473,750 discloses the purification of waste water from coke plants. The waste water contains various substances, including phenol, cresol, hydrocyanic acid, hydrogen sulphide, thiocyanates and calcium salts. The disclosed purification process includes the steps of neutralizing the waste water with sulfuric acid, allowing the neutralized waste water to stand so that the salts formed can precipitate out, decanting the liquid from the precipitate, and contacting the recovered liquid with coke oven gas. The materials in the precipitate are not separated out or selectively recovered.
U.S. Pat. No. 4,491,677 discloses the use of a phenolic compound and a solvent to crystalize a particular cresol from a mixture of cresols obtained from refinery waste streams. The procedure involves contacting the cresol mixture with a phenolic compound and solvent and thereafter allowing the solution to stand and cool so that the desired cresol precipitates.
U.S. Pat. No. 2,275,045 discloses a preparation for phenolic compounds wherein the phenols are initially obtained in the form of a metal salt such as calcium phenate. The phenol is recovered by acidifying the reaction mixture with a strong mineral acid to decompose the calcium phenate so that the phenol can be steamed distilled from the acidified mixture.
U.S. Pat. No. 4,746,443 discloses a process of purification of waste water containing bentazon involving the decomposition of the bentazon. The process includes the adjustment of the waste water pH to a level between 0.2 and 7 utilizing an acid, such as sulfuric acid, followed by the heating of the acidified waste water to at least 60.degree. C. The water is neutralized with an alkaline material prior to discharge.
The art does not disclose affecting the solubility of a nitrophenolic by-product contained in nitration waste water, which is made up of a plurality of nitrophenolic by-products, utilizing an acid to selectively recover the nitrophenolic by-product in substantially pure form by precipitation. Furthermore, the art does not disclose a process of recovering a nitrophenolic by-product from nitration waste water in a form suitable for commercial sale.
The ability to selectively recover a particular nitrophenolic by-product in substantially pure form from nitration waste water utilizing an acid is surprising in that while an acid has been used in the past to precipitate nitrophenolic compounds, the prior art methods require additional purification steps to obtain any particular nitrophenol in a substantially pure form. According to the prior art methods, the acid indiscriminately precipitates all materials. Where additional purification steps have not been used, it was because only an isomeric mixture of nitrocresols was acted upon by an acid rather than a mixture of varying nitrophenolic compounds such as present in nitration waste water. Selective precipitation based on the pH control of a mixture of isomeric and nonisomeric nitrophenolic materials, which does not require additional purification steps, is an important economic and environmental advance.